Process and apparatus for washing residual solvent from as-spun polybenzimidazole continuous filamentary materials

ABSTRACT

An improved process and apparatus for the washing of residual solvent from as-spun polybenzimidazole continuous filamentary materials (e.g., monofilament and multifilament strand, cable, yarn, tow, etc.) are disclosed. The material is passed onto one end of one roller of a pair of spaced rollers within a washing tank. The material is wound about the pair of rollers through a generally helical path and exits off of the other end of the pair of rollers. The rollers are at least partially immersed in a heated washing liquid. Wiper bars are located within the washing tank to wipe surface bubbles from the continuous filamentary material during washing to increase the efficiency of the washing step. Washing is achieved in a matter of minutes as opposed to hours in prior procedures. Two or more adjacent pairs of rollers in one or more tanks may be utilized with the material being advanced from one pair of rollers to another pair, preferably while immersed in the washing liquid.

United States Patent [1 1 Prince, Jr.

[451 July 3,1973

[ PROCESS AND APPARATUS FOR WASHING RESIDUAL SOLVENT FROM AS-SPUN POLYBENZIMIDAZOLE CONTINUOUS FILAMENTARY MATERIALS [75] Inventor: Arthur E. Prince, Jr., Basking Ridge,

[73] Assignee: Celanese Corporation, New York,

[22] Filed: Mar. 31, 1972 [21] Appl. No.: 239,973

Primary Examiner-William 1. Price Attorney-Thomas J. Morgan, Charles B. Barris et al.

[5 7] ABSTRACT An improved process and apparatus for the washing of residual solvent from as-sp un polybenzimidazole continuous filamentary materials (e.g., monofilament and multifilament strand, cable, yarn, tow, etc.) are disclosed. The material is passed onto one end of one roller of a pair of spaced rollers within a washing tank. The material is wound about the pair of rollers through a generally helical path and exits off of the other end of the pair of rollers. The rollers are at least partially immersed in a heated washing liquid. Wiper bars are locatedwithin the washing tank to wipe surface bub bles from the continuous filamentary material during washing to increase the efficiency of the washing step.

- Washing is achieved in a matter of minutes as opposed to hours in prior procedures. Two or more adjacent pairs of rollers in one or more tanks may be utilized with the material being advanced from one pair of rollers to another pair, preferably while immersed in the washing liquid.

22 Claims, 5 Drawing Figures PAIENTEDJUL 31m 3.7435479 He. i

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O F A l 0 N Q 4A akmams PATENIEB ill 3 I973 FIG. 4

PROCESS AND APPARATUS FOR WASHING RESIDUAL SOLVENT FROM AS-SPUN POLYBENZIMIDAZOLE CONTINUOUS FILAMENTARY MATERIALS BACKGROUND OF THE INVENTION The manufacture of polybenzimidazole continuous filamentary materials, e.g., monofilament and multifilament yarn, strand, tow, cable and the like is well known in the art. A solution of polybenzimidazole in an appropriate solvent is formed into a continuous filamentary material such as yarn, by known procedures, such as spinning, and the material is washed. The washed material is dried and subsequently drawn.

The as-spun polybenzimadazole continuous filamentary material contains a residual amount, e.g., from about 5 to about 25 percent by weight of the material, of the forming solution. This residual solvent must be removed before the material may be satisfactorily drawn. Drawing of polybenzimidazole continuous filamentary materials is a well known method for increasing the tensile properties, and particularly tenacity, of the materials. It has been found, however, that polybenzimidazole continuous filamentary materials often explode during a drawing operation resulting in a porous product having relatively low tensile properties.

The explosion problem is believed due in large part to the presence of residual solvent or other moisture in the polybenzimidazole continuous filamentary materials. The removal of the solvent is therefore necessary. It has been found that even small amounts of residual spinning solvent have a very detrimental effect on the final properties of the finished material. Residual spinning solvent permits non-orientation of the molecules of the material thus interfering with the physical properties of the material.

Residual solvent is generally removed by washing. For example, as disclosed in U.S. Pat. No. 3,584,104, as-spun polybenzimidazole fiber may be washed until it contains less than 0.1 percent by weight of the solvent and preferably until the material is essentially free of the solvent. Heretofore, washing has been conducted by winding the polybenzimidazole fiber or other continuous filamentary material on perforated rollers or bobbins, immersing the wound bobbins in liquid wash medium and pressure washing the fiber for about 2 to 100 hours or more. Pressure washing is accomplished by passing the wash medium through the interior of the hollow, perforated bobbin and outwardly through'the perforations so that the solvent is flushed from the polybenzimidazole material wound thereon. Typically, a water wash may be used although other wash liquids such as acetone, methanol, methylethylketone or other materials may be used. The washed fiber is then dried to remove the wash liquid. It has heretofore been generally necessary to subject as-spun polybenzimidazole continuous filamentary materials to a slight steam drawing treatment at a draw ratio of from about l.05:l to l.5l:lin order to prevent the materials from relaxing and falling off the bobbin during washing.

Pressure washing is an expensive and timeconsuming operation, requiring time to wind the bobbins and a considerable time to wash the material. In addition, the pressure washing operation is not particularly suitable for use in continuous, in-line processes. Although large amounts of polybenzimidazole continuous filamentary material may be wound on one bobbin,

around the continuous filamentary material to flush out the solvent.

Pressure washing also requires the utilization, for any substantial amounts of continuous filamentary-materials, of relatively large numbers of the aforesaid perforated bobbins as well as other necessary apparatus. A large equipment expenditure and inventory is thus required.

It is an object of this invention to provide a process and apparatus for washing polybenzimidazole continuous filamentary materials in a relatively quick and inexpensive manner.

It is further an object of this invention to provide a process and apparatus for washing polybenzimidazole continuous filamentary materials which are adapted to remove substantial amounts of residual forming solvent from the materials in a relatively short time.

It is also an object of this invention to provide a process and apparatus for washing polybenzimidazole continuous filamentary materials in which a prior steam drawing treatment is not necessary.

These and other objects, as well as the scope, nature and utilization of the invention will be apparent from the following detailed description and appended claims.

SUMMARY OF THE INVENTION These and other objects of the invention are achieved in one aspect by a method for washing polybenzimidazole continuous filamentary materials which comprises: feeding the said polybenzimidazole continuous filamentary material in the direction of its length to one end of a pair of spaced wash rollers at least partially immersed in a washing liquid; passing the said polybenzimidazole continuous filamentary material in the direction of its length along a generally helical path having a multiplicity of turns towards the opposite end of the said pair of rollers with the said path being substantially suspended within the said washing liquid when passing between each of said spaced rollers; wiping said polybenzimidazole continuous filamentary material to remove surface bubbles therefrom when passing between each of said spaced rollers; and passing washed polybenzimidazole continuous filamentary material off from the said opposite end of the said pair of rolers.

In another aspect, the present invention provides apparatus for washing polybenzimidazole continuous filamentary material comprising: a washing tank adapted to contain a washing liquid, at least one pair of spaced wash rollers providing traversal path guiding means for the said material during washing whereby the said material is washed for a predetermined time, means for introducing said material onto a first end of one roller of the said roller, means for removing the washed material from the second end of one of said rollers, and wiper means disposed within said tank to'contact said material during washing to remove surface bubbles therefrom.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a schematic representation of one emebodiment of an apparatus arrangement of the invention;

FIG. 2 is a view along line A-A of FIG. 1;

FIG. 3 is a view similar to FIG. 2 along line AA of a second embodiment of the apparatus arrangement of FIG. 1;

FIG. 4 is a top view of a schematic representation of another embodiment of an apparatus arrangement of the invention; and

FIG. 5 is a view along line BB of FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS The Starting Polymer Polybenzimidazoles are a known class of heterocyclic polymers which consist essentially of recurring units of the following formulas I and II. Formula I is:

wherein R is a tetravalent aromatic nucleus, with the nitrogen atoms forming the benzimidazole rings being paired upon adjacent carbon atoms, i.e., ortho carbon atoms, of the aromatic nucleus, and R is a member of the class consisting of an aliphatic (alkylene) group, a cycloaliphatic ring, an aromatic ring and a heterocyclic ring such as pyridine, pyrazine, furan, quinoline, thiophene, and pyran.

Formula II is:

wherein Z is an aromatic nucleus having the nitrogen atoms forming the benzimidazole ring paired upon adjacent carbon atoms of the aromatic nucleus.

Preferably, the continuous filamentary materials are prepared from aromatic polybenzimidazoles, that is, from polymers consisting essentially of the recurring units of Formula II and of Formula I wherein R is an aromatic ring or a heterocyclic ring.

As set forth in the United States Pat. No. 3,174,947 and U.S. Pat. No. Re. 26,065, which are incorporated herein by reference, the aromatic polybenzimidazoles having the recurring units of Formula Il may be prepared by self-condensing a trifunctional aromatic compound contuining only a single set of ortho disposed diamino substitutents and an aromatic, preferably phenyl, carboxylate ester substituent. Exemplary of polymers of this type is poly-2, 5(6)-benzimidazole prepared by the auto-condensation of phenyl-3,4- diaminobenzoate.

As also set forth in the above-mentioned patents, the aromatic polybenzimidazoles having the recurring units of Formula I may be prepared by condensing an aromatic tetraamine compound containing a pair of orthodiamino substituents on the aromatic nucleus with a dicarboxylie compound selected from the class consisting of (a) the diphenyl ester of an aromatic dicarboxylic acid, (b) the diphenyl ester of a heterocyclic discarboxylie acid wherein the carboxyl groups are substituents upon carbon in a ring compound selected from the class consisting of pyridine, pyrazine, furan, quinoline, thiophene and pyran and (c) an anhydride of an aromatic dicarboxylic acid.

Examples of aromatic polybenzimidazoles which have the recurring structure of Formula I and which may be formed into fibers or yarns include:

poly-2,2 (m-phenylene)-5,5'-bibenzimidazole;

poly-2,2'-(pyridylene-3",5")-5,5-bibenzimidazole;

poly-2,2'-(furylene-2,5")-5,5'-bibenzimidazole; poly-2,2'-(naphthalene-l ",6")-5,5'-

bibenzimidazole; poly-2,2'-(biphenylene 5,5bibenzimidazole; poly-2,2'-amylene-5,5'-bibenzimidazole; poly-2,2-octamethylene-5,5'bibenzimidazole; poly-2,6-(m-phenylene)-dimidazobenzene; poly-2,2'-cyclohexenyl-5,5'-bibenzimidazole; poly-2,2'(m-phenylene)-5,5'-di(benzimidazole) ethpoly-2,2(m-phenylene)-5,5'-di(benzimidazole)sulfide;

poly-2,2(m-phenylene)-5,5-di(benzimidazole) sulfone;

poly-2,2'(m-phenylene)-5,5'-

di(benzimidazole)methane;

poly-2,2"(m-phenylene)-5', ,5"di(benzimidazole)- propane-2,2; and

poly-2',2" (m-phenylene)-5', 5" di(benzimidazole)ethylene-l ,2 where the double bonds of the ethylene groups are intact in the final polymer.

The preferred aromatic polybenzimidazole fiber or yarn is one prepared from poly-2,2-(m-phenylene)- -5,5'-bibenzimidazole, the recurring unit of which is:

Any polymerization process known to those skilled in the art may be employed to prepare the polybenzimidazole which may then be formed into a continuous filamentary material and subjected to the treatment of the present invention. Preferred techniques used to prepare the polybenzimidazole are disclosed in US. Pat. Nos. 3,509,108 and 3,551,389, both assigned to the assignee of the present invention and both herein incorporated by reference.

With respect to aromatic polybenzimidazoles, preferably equimolar quantitiesof the monomeric tetraamine and dicarboxyl compound are introduced into a first stage melt polymerization reaction zone and heated therein at a temperature above about 200C., preferbaly at least 250C, and more preferably from about 270 to 300C. The reaction is conducted in a substantially oxygen-free atmosphere, i.e., below about 20 ppm oxygen and preferably below about 8 ppm oxygen, until a foamed prepolymer is formed. Usually, the first stage reaction is continued until a prepolymer is formed having an inherent viscosity, expressed as deciliters per gram, of at least 0.1 and preferably from about 0.l3 to 0.3, the inherent viscosity (I.V.) as used in the present specification and claims being determined from a solution of 0.4 grams of the polymer in 100 ml. of 97 precent H SO at 25C.

After the conclusion of the first stage reaction, which normally takes at least 0.5 hours, and preferably 1 to 3 hours, the foamed prepolymer is cooled and then powdered or pulverized in any convenient manner. The resulting prepolmer powder is then introduced into a second stage polymerization reaction zone wherein it is heated under substantially oxygen-free conditions, as described above, to yield a polybenzimidazole polymer product, desirably having an I.V., as measured above, of at least 0.6, e.g., 0.80 to 1.1 or more. i

The temperature employed in the second stage is at least 250C., preferably at least 325C, and more preferably from about 350 to 425C. The second stage reaction generally takes at least 0.5 hours, and preferably from about 1 to 4 hours or more.

A preferred method of preparing the polybenzimidazole is disclosed in the aforesaid U.S. Pat. No. 3,509,108. As disclosed therein, aromatic polybenzimidazoles may be prepared by initially reacting the monomer in a melt phase polymerization at a temperature above about 200C. and a pressure above about 50 psi (e.g., 300 to 500 psi) and then heating the resulting reaction product in a solid state polymerization at a temperature above about 300C. (e.g., 350 to 500C. to yield the final product.

Preparation of the Continuous Filamentary Material The term continuous filamentary material as used herein is intended to include monofilaments and multifilaments such as strand, yarn, cable, tow and the like.

As is well known, the polybenzimidazoles are generally formed into continuous filamentary materials by solution spinning, that is, by dry or wet spinning a solution of the polymer in an appropriate solvent such as dimethylacetamide, dimethylformamide, dimethylsulforide or sulfuric acid (used only in wet spinning) through an opening of predetermined shape into an evaporative atmosphere for the solvent in which most of the solvent is evaporated (dry) or into a coagulation bath (wet), resulting in the polymer having the desired shape.

The polymer solutions may be prepared, for example, by dissolving sufficient polybenzimidazole in the solvent to yield a final solution suitable for'extrusion containing from about to 45 percent by weight of polymer, based on the total weight of the solution, preferably from about 20 to 30 percent by weight.

One suitable means for dissolving the polymer in the solvent is by mixing the materials at a temperature above the atmospheric boiling point of the solvent, for example, 25 to 120C. above such boiling point, and at a pressure of 2 to atmospheres for a period of l to 5 hours; Preferably, the above polymer solutions, after suitable filtration to remove any undissolved portions, are dry spun. For example, the solutions may be extruded through a spinneret into a conventional type downdraft spinning column containing a circulating inert gas such as nitrogen, noble gases, combustion gases or super heated steam. Conveniently, the spinneret face is at a temperature of from about 100 to 170C., the top of the column from about 120 to 220C., the middle of the column from about 140 to 250C., and the bottom of the column from about 160 to 320C. After leaving the spinning column, the contin'uous filamentary materials can be taken up, for example, at a speed in the range of from about 50 to 350meters per minute. Further details for a method of dry-spinning polybenzimidazole continuous filamentary materials are shown in U.S. Pat. No. 3,502,756, Bohrer et a1, assigned to the same ass'ignee as the present application, and this patent is hereby incorporated by reference.

The as-spun continuous filamentary material yarns may be collected to form a tow of larger denier which may then be washed so as to remove at least the major portion of residual spinning solvent, e.g., so that the washed materials contain'less than about 0.5 percent by weight, preferably less than about 0.1 percent by weight, solvent based on the weight of the continuous filamentary material, and preferably so as to obtain an essentially spinning solvent free continuous filamentary material.

The continuous filamentary material is passed into a washing zone including a washing tank containing a wash liquid and at least one pair of spaced wash rollers at least partially immersed in the wash liquid. The wash liquid typically and preferably will be water, although other wash liquids such as acetone, methanol, methyl ethyl ketone or the like may be utilized. The material enters the washing tank and is passed about one end of one roller of a pair of spaced rollers and passed about the pair of rollers in a generally helical fashion such that the material progresses through a generally helical traverse of the wash liquid. When the material reaches the opposite end of the pair of rollers, it may be taken off and passed out of the washing tank. The washing liquid is circulated in the washing tank while it is in contact with the polybenzimidazole continuous filamentary material. Preferably, the washing liquid is heated and, most preferably, is heated to a temperature of about 5C. below its boiling point at atmospheric pressure.

The rollers utilized in the washing tank of this invention are arranged so as to provide a controlled traversal path guide for the material through the washing liquid without overlapping or jamming together of adjacent portions of the material. Thus, in one embodiment of the invention, the rollers have helically extending grooves formed therein to provide the traversal path for the material while maintaining adjacent revolutions of material separate from each other. In another em bodiment, the rollers may have a smooth (i.e., ungrooved) surface but each pair of rollers is arranged in a converging or skewed relationship. That is, the rollers converge slightly toward each other at the delivery or take-off (preferably take-off) end. Smooth-surfaced, skewed rollers are preferred. The rollers may be formed of any suitable material which is nondeleterious to the polybenzimidazole continuous filamentary materi'aland not attacked by the wash liquid "or inorganic stabilizer materials which may be'present The washing zone 1 includes a washing tank 12. Contained within the washing tank 12 are a pair of spaced, skewed, smooth-surfaced rollers 3 and 4 immersed within the wash liquid 5. The rollers 3 and 4 generally converge, as known in the art, at an angle sufficient to enable uniform tacking of the material Without overlap and to maximize the number of wraps on the set of rollers. As shown in FIG. 2, the convergence may be accomplished by vertically offsetting one roller, such as roller 4, the desired angular amount (a). Alternatively, each of rollers 3 and 4 may be vertically offset in angular amounts sufficient to yeild the desired convergence of the pair of rollers. Rollers 3 and 4 are supported by suitable support means (not shown). These rollers are provided with a suitable power means (not shown) to drive both of the rollers at the same rotational velocity.

The polybenzimidazole continuous filamentary material 2 enters the tank 12 and is passed in the direction of its length in contact with a first end of roller 3 and then passed in the direction of its length about the upper (or first) end of the pair of spaced converging rollers 3 and 4. Preferably, the upper end is that end at which the rollers 3 and 4 are spaced the farthest apart. The material 2 is then passed in the direction of its length about the spaced converging rollers 3 and 4 in a generally helical'manner and advanced in the direction of its length towards the lower (or second) end of the pair of spaced converging rollers 3 and 4. Wiper bars 7 and 8 may be located within the tank 12, advantageously adjacent the spaced converging rollers 3 and 4, respectively, to lightly contact the surface of the material 2 and remove bubbles from the surface of the material 2. Wiper bars 7 and 8 may be formed of any suitable non-deleterious material such as stainless steel, ceramic, solid fluorinated hydrocarbons (Teflon) or the like.

The material 2 is taken off in the direction of its length from the bottom or second end of roller 4 and then out of tank 12 and washing zone 1. The washed material may be subjected to further processing as ex plained below (not shown). Suitable guide means l4, l and 16 may be utilized to assist in guiding the material 2 into, through and out of the washing zone 1.

The washing tank 12 has a wash liquid takeoff indicated as 9 and an intake 10 where makeup wash liquid may be added. The circulatory flow of the wash liquid 5 through the washing tank 12 may be carried out with suitable pumping means (not shown). Temperature in the washing tank may be maintained by adding the wash liquid to the tank at an elevated temperature. Alternatively, the washing tank 12 may contain appropriate heating means such as steam tubes 11 disposed in the bottom of the washing tank 12 in which steam is circulated from a steam generator and pump system outside of the tank and not illustrated.

FIG. 3 illustrated another embodiment of the washing zone of the invention. The view shown in FIG. 3 is similar to that of FIG. 2 and similar portions or members are numbered with prime numerals. In the embodiment shown in FIG. 3, however, rollers 3' and 4 contain a plurality of helical grooves 17' and 18 which define the traversal path for polybenzimidazole continuous filamentary material 2'. The material 2' seats in the grooves 17' and 18 as it passes about the rollers 3' and 4' in the direction of its length. In this embodiment, rollers 3' and 4 may be arranged in either a parallel or skewed relationship. Also, the rollers 3' and 4' of this embodiment are preferably independent rollers, that is, they are not connected to external power means or to each other and are rotationally driven only by the forces applied by the moving material 2.

The washing tank may also contain more than one pair of spaced rollers. For example, it may be desirable that at least two pair of spaced rollers be utilized with the continuous filamentary material passing in the direction of its length from one end of one roller of one of the said pairs to one end of one roller of another of the said pairs. Three or more pairs of spaced rollers may be utilized with a similar system of passing of the material in the direction of its length from one end of one roller of one pair to one end of one roller of another pair.

FIGS. 4 and 5 show a preferred arrangement of a washing zone 21 utilizing two pair of spaced rollers. In the embodiment shown, each pair of spaced rollers are skewed, smooth-surfaced rollers of the type shown above in the embodiment of FIGS. 1 and 2. The polybenzimidazole continuous filamentary material 22 enters the washing tank 23 and is passed in the direction of its length about the upper end of roller 24 which is one of a pair of spaced, skewed, smooth-surfaced rollers 26 and 27. Each pair of spaced converging rollers 24 and 25 and 26 and 27 converges at the same angle (a) and each pair also converges such that the upper (or first) ends of the rollers are spaced farthest apart. Each of the rollers are connected to suitable power means (not shown) such that all of the rollers may be driven at the same rotational velocity. The washing tank 23 may also be equipped with a divider 28 between each pair of spaced converging rollers to sepa rate the washing tank 23 into compartments 29 and 30 with each compartment containing one pair of rollers. The divider 28 has an opening or separation 39 such that the continuous filamentary material 22 may advance in the direction of its length from one pair of spaced converging rollers to the other pair of rollers while remaining in the washing tank 23 (and preferably while immersed in the washing liquid) as further described hereinbelow. The opening 39 also provides a fluid communication path between the compartments 29 and 30.

Wiper bars 31 and 32 are disposed in wash compartment 29 to lightly contact the surface of the polybenzimidazole continuous filamentary material as it is traversing in the direction of its length about rollers 24 and 25 and to remove bubbles appearing on the surface of the material. Wiper bars 33 and 34 are similarly dis posed in compartment 30 adjacent rollers 26 and 27, respectively, and for the same purpose.

Washing tank 23 may be maintained at the washing temperature by adding heated washed liquid. Alternatively, and as set forth above in regard to FIGS. 1 and 2, steam tubes 35 may be disposed in the bottom of the washing tank 23. Wash liquid inlet and outlet means 36 and 37 are provided such that the flow of wash liquid 38 in the washing tank 23 is countercurrent to the general direction of movement of the material 22.

The material22 enters the washing zone 21 and is passed about the first end of one roller of the first pair of rollers (24 and 25) in the same manner as material 2 shown in FIG. 2 and explained above. In this embodiment, however, the material 22 passes from the second end of the first pair of rollers, through the opening 39 and onto one end of the second pair of rollers (26 and 27). The material passes about the second pair of rollers traversing a generally helical path through the washing liquid 40. When the material approaches the other end of the second pair of rollers, it may be taken off and passed out of the washing zone for further processing.

It should be recognized, and will be obvious to those skilled in the art, that more than two pair of rollers may be utilized and also that, regardless of the number of rollers, grooved independent idler rollers such as illustrated in the embodiment of FIG. 3 may be substituted for the converging, smooth-surfaced rollers shown and described herein.

It will also be understood by those skilled in the art that each pair of rollers may be disposed in a separate washing tank. In this embodiment, the material will be passed from one end of a first pair of rollers in a first washing tank out of the tank, into a second washing tank and onto a first end of a second pair of rollers. The travel of the polybenzimidazole continuous filamentary material through each washing tank is performed in the manner set forth above.

With any of the apparatus embodiments shown in FIGS. 1 through 5, the filamentary material is passed in the direction of its length through the wash liquid at a speed and for a time sufficient to reduce the residual spinning solvent of the material to below about 0.5 percent of weight of the filament and preferably such that the material is essentially solvent-free (that is, less than about 0.1 pecent). For example, the continuous fila mentary material may be passed in the direction of its length through the washing zone at a speed of from about 1 to about 50, preferably from about 10 to about 25, meters per minute for at least 1 minute, preferably from about 1 to about 20 minutes, most preferably from about 4 to about 15 minutes.

The washed continuous filamentary material may be dried to remove the washing liquid and then drawn. For example, the polybenzimidazole continuous filamentary material may be heated or'otherwise treated to remove residual washing liquid down to a level sufficient to allow the material to be drawn without substantial explosion problem, e.g., less than about 2.0 percent, preferably less than about 0.1 percent by weight of the material. The washed material may be passed, for example, into contact with a heated contact surface, hot gas zone, heated oven or furnace or otherwise treated in any suitable manner as may be apparent to those skilled in the art.

Drawing of the polybenzimidazole continuous filamentary materials may be performed in any suitable manner according to drawing procedures known to those skilled in the art. Particularly preferred drawing techniques are disclosed in U.S. Pat. No. 3,622,660 of George F. Ecker and Thomas C. Bohrer and U.S. Pat.v No. 3,541,199 of Thomas C. Bohrer and Arnold .1. R- senthal. Both of these patents are assigned to the same assignee as the present invention and are herein incorporated by reference.

Preferably, the continuous filamentary material is passed immediately from the drying step into the hot drawing zone in order to minimize exposure of the material to the atmosphere.

The polybenzimidazole continuous filamentary materials may, for example, be drawn at high drawing speeds, that is, the speed of the supply roll may be on the order of to 50 meters per minute or higher. The

limiting factor of the drawing speed is the particular design of the drawing apparatus and the elastic properties of the fiber. 5 The polybenzimidazole continuous filamentary materials may be subjected to a hot drawing treatment in any convenient hot drawing apparatus or zone, for example, by passing the material over a heated surface such as a hot roll, shoe, pin or plate or by passing the material through a radiantly heated zone, such as a muffle furnace.

Hot drawing is suitably conducted at a temperature of above about 350 C. up to about the degradation temperature of the polybenzimidazole continuous filamentary material, preferably from about 375to 650 C., and more preferably from about 390 to 480 C.

The polybenzimidazole continuous filamentary materials may be drawn at any desired draw ratio below that at which they break, typically from above about 1.5:1 to 4.521, and preferably from about 2.511 to 3.511. The hot drawing residence time, i.e., the time during which the material is being heated, is usually from about 0.2 to 50 seconds, preferably 0.5 to 10 seconds, and more preferably 0.5-to 5 seconds. Substantially longer residence times at the elevated drawing temperatures may cause degradation. Other suitable polybenzimidazole drawing techniques will be apparent to those skilled in the art.

The process and apparatus of this invention are particularly adapted for use in conjunction with my continuous drying and drawing process disclosed and claimed in my copending U.S. Pat. application Ser. No 239,898, entitled Drying, and Drawing Process for Polybenzimidazole Continuous Filamentary Materials, filed of even date herewith, assigned to the same assignee and herein incorporated by reference.

It will be understood by those skilled in the art that the process and apparatus of this invention can be practiced with a horizontal arrangement of the washing zone (e.g., with the rollers oriented horizontally) as well as the vertical arrangements illustrated in the Figures.

The resulting drawn polybenzimidazole continuous filamentary materials of the present invention are characterized by a high degree of thermal stability and show great resistance to degradation by heat, hydrolytic media and oxidizing media. They may be used, for example, in deceleration chutes for aircraft, chutes for re-entry capsules, high temperature dust collector bags, non-flammable clothing and fabric and in spacesuits and flight clothing.

The invention will be further described with reference to the following examples which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the examples.

EXAMPLE I A polybenzimidazole yarn, namely, poly-2,2'-(mphenylene)- 5,5'-bibenzimidazole, is selected as the exemplary polybenzimidazole for use in exemplifying the invention.

The polymer is formed into an as-spun yarn in the manner described in Example I of U.S. Pat. No. 3,502,756 to Bohrer et al. More particularly, a dope of dimethylacetamide containing 23 percent by weight of the polymer is extruded through a 1l0-hole jet into a dry spinning chamber containing super-heated steam as the drying atmosphere. A 600/200 yarn (200 filaments making up a yarn having an overall denier of 600) is formed from the as-spin yarn. The yarn contains. about 15 percent by weight of the material of residual dimethylacetamide. Five ends of the yarn are plied to form a 2700/990 tow.

The apparatus of FIG. 3 is utilized in immersion washing of the as-spun tow except that some runs are performed without the wiper bars 7 and 8' being utilized to contact the surface of the yarn. Water is used as the wash liquid. Residence time and bath temperature are varied and the residual amount of dimethylacetamide solvent in each washed sample is measured. The results are shown below in Table I.

As may be seen, samples treated at higher temperatures of the wash liquid and longer residence times have lower residual solvent content.

It is noted that surface bubbles form on the yarn as it passes through the wash liquid. The utilization of the wiper bars to lightly contact the yarn and to remove these surface bubbles results in a significant reduction of residual spinning solvent content in a relatively short time. Compare Runs 9 and 10 with Runs 14 and 15. All of these runs are made under identical conditions except that wiper bars 7 and 8' are used in the latter runs. The residual solvent content of both runs 14 and 15 is about one-quarter of that of runs 9 and 10.

However, tension buildup on the grooved rollers results in a significant level of broken filaments. Also, the grooves tend to bundle the yarn even when flat bands of yarn are provided as the as-spun starting material.

Similar runs which are made with the same yarn and under identical conditions with the apparatus of FIGS. 1 and 2 containing a pair of smooth-surfaced, skewed rollers yield substantially the same results with regard to residual solvent content. The number of broken filaments is substantially reduced as compared to identical runs on grooved rollers and there is a substantially lessened tendency to bundle flat bands of yarn.

TABLE I Residual Solvent after Residence Bath Washing, Weight EXAMPLE II The polybenzimidazole of Example I is formed into yarn containing 990 filaments, 2,970 filaments and 4,950 filaments. Each yarn contains about 15 percent by weight of the yarn of residual dimethylacetamide spinning solvent. Each of the yarns is washed in the apparatus of FIGS. 4 and 5. The yarn speed through the washing tank as well as the yarn residence time therein are varied. The test conditions and results obtained are shown below in Table II. The residual solvent level generally decreases with increasing residence time and decreasing yarn speed.

TABLE II Residual Solvent Level Residence Yarn After Washing, Weight Percent Time Speed 990 2970 4950 (min) (m/min) filaments filaments filaments 16.5 3 0.05 0.06 0.07

EXAMPLE III The effect of residence time on removal of residual spinning solvent from the yarn of Example I is measured by washing the yarn at varying speeds through a washing zone of constant length and by varying the length of the washing zone at a constant residence time. The yarn has an initial residual dimethylacetamide spinning solvent content of 15 percent by weight of the yarn. The test conditions and results obtained are shown below in Table III.

TABLE III Residence Residual Yarn speed Time Spinning Solvent (m/min) Zone (meters) (minutes) Percent by Weight 1.0 25 25 0.02 5.0 25 5 0.01 12.5 25 2 0.03 37.8 78.6 2 0.08

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the present invention.

I claim:

1. A method for washing polybenzimidazole continuous filamentary material which comprises:

feeding said polybenzimidazole continuous filamentary material in the direction of its length to one end of a pair of spaced wash rollers at least partially immersed in a washing liquid;

passing said polybenzimidazole continuous filamentary material in the direction of itslength along a generally helical path having a multiplicity of turns towards the opposite end of the said pair of rollers with said path being substantially suspended within the said washing liquid when passing between each of said spacing rollers;

wiping said polybenzimidazole continuous filamentary material to remove surface bubbles therefrom when passing between each of said spaced rollers, and

passing washed polybenzimidazole continuous filamentary material off from the said opposite end of the said pair of rollers.

2. The method of claim 1 wherein said washing liquid is heated to a temperature within about 5 C. of its boiling point.

3. The method of claim 1 wherein said washing liquid is circulated while in contact with said polybenzimidazole continuous filamentary material.

4. The method of claim 1 inwhich said spaced wash rollers are two independent idler rollers having grooves therein in which thesaid material travels.

5. The method of claim 1 in which said spaced wash rollers are two skewed, smooth-surfaced rollers.

6. A method for washing as-spun polybenzimidazole continuous filamentary materials to remove residual spinning solvent which comprises:

introducing said as-spun polybenzimidazole continuous filamentary material containing a substantial quantity of residual spinning solvent into a washing zone which includes at least one pair of spaced wash rollers and a washing liquid circulating within said washing zone;

causing said polybenzimidazole continuous filamentary material to successively travel about one-of said rollers and then another of said rollers to define a generally helical traversal path, the generally helical traversal path being immersed in said wash liquid;

wiping said polybenzimidazole continuous filamentary material to remove surface bubbles therefrom when passing between said pair of spaced rollers,-

and removing the resulting washed polybenzimidazole continuous filamentary material from the washing zone having a residual spinning solvent content less than about 0.5 percent by weight.

7. The method of claim 6 in which said spaced wash rollers are independent idler rollers having grooves therein in which the said material travels.

8. The method of claim 6 in which said spaced wash rollers are skewed, smooth-surfaced rollers.

9. The method of claim 8 in which each roller is driven at the same rotational velocity.

10. The method of claim 6 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone at a speed of from about 1 to about 50 meters per minute.

11. The method of claim 10 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone at a speed of from about 10 to about 25 meters per minute.

12. The method of claim 10 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone for a time of at least about 1 minute.

13. The method of claim 12 wherein said polyben zimidazole continuous filamentary material is passed to about 20 minutes.

14. The method of claim 13 wherein said polybenzimidazole continuous filamentary material is passed through said, washing zone for a time of from about 4 to about 15 minutes.

15. The method of claim 14 wherein said washing liquid is water.

16. Apparatus for washing polybenzimidazole continuous filamentary material comprising:

a washing tank adapted to contain a washing liquid,

at least one pair of spaced wash rollers providing traversal path guiding means for the said materialduring washing whereby the said material is washed for a predetermined time, means for introducing said material onto a first end of one roller of said rollers, means for removing the washing material from the second end of one of said rollers, and wiper means disposed within said tank to contact said material during washing to remove surface bubbles therefrom.

17. The apparatus for claim 16 further including means for conducting a circulatory flow of washing liquid within the washing tank.

18. The apparatus of claim 17 further including means for heating washing liquid.

19. The apparatus of claim 17 in which each roller contains grooves therein to'define the said traversal path guiding means.

20. The apparatus of claim 17 in which each roller is smooth surfaced and each pair of rollers is skewed.

21. The apparatus of claim 20 further including power means to drive each roller in each said pair of rollers at the same rotational velocity.

22. The apparatus of claim 16 wherein said washing tank includes a dividing means to separate the said tank into two washing areas connected by an opening, each washing area containing a pair of spaced, skewed, smooth-surfaced rollers, said washing tank further including means for introducing the said material from the second end of the first pair of roller onto the first end of the second pair of rollers. 

2. The method of claim 1 wherein said washing liquid is heated to a temperature within about 5* C. of its boiling point.
 3. The method of claim 1 wherein said washing liquid is circulated while in contact with said polybenzimidazole continuous filamentary material.
 4. The method of claim 1 in which said spaced wash rollers are two independent idler rollers having grooves therein in which the said material travels.
 5. The method of claim 1 in which said spaced wash rollers are two skewed, smooth-surfaced rollers.
 6. A method for washing as-spun polybenzimidazole continuous filamentary materials to remove residual spinning solvent which comprises: introducing said as-spun polybenzimidazole continuous filamentary material containing a substantial quantity of residual spinning solvent into a washing zone which includes at least one pair of spaced wash rollers and a washing liquid circulating within said washing zone; causing said polybenzimidazole continuous filamentary material to successively travel about one of said rollers and then another of said rollers to define a generally helical traversal path, the generally helical traversal path being immersed in said wash liquid; wiping said polybenzimidazole continuous filamentary material to remove surface bubbles therefrom when passing between said pair of spaced rollers; and removing the resulting washed polybenzimidazole continuous filamentary material from the washing zone having a residual spinning solvent content less than about 0.5 percent by weight.
 7. The method of claim 6 in which said spaced wash rollers are independent idler rollers having grooves therein in which the said material travels.
 8. The method of claim 6 in which said spaced wash rollers are skewed, smooth-surfaced rollers.
 9. The method of claim 8 in which each roller is driven at the same rotational velocity.
 10. The method of claim 6 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone at a speed of from about 1 to about 50 meters per minute.
 11. The method of claim 10 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone at a speed of from about 10 to about 25 meters per minute.
 12. The method of claim 10 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone for a time of at least about 1 minute.
 13. The method of clAim 12 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone for a time of from about 1 to about 20 minutes.
 14. The method of claim 13 wherein said polybenzimidazole continuous filamentary material is passed through said washing zone for a time of from about 4 to about 15 minutes.
 15. The method of claim 14 wherein said washing liquid is water.
 16. Apparatus for washing polybenzimidazole continuous filamentary material comprising: a washing tank adapted to contain a washing liquid, at least one pair of spaced wash rollers providing traversal path guiding means for the said material during washing whereby the said material is washed for a predetermined time, means for introducing said material onto a first end of one roller of said rollers, means for removing the washed material from the second end of one of said rollers, and wiper means disposed within said tank to contact said material during washing to remove surface bubbles therefrom.
 17. The apparatus for claim 16 further including means for conducting a circulatory flow of washing liquid within the washing tank.
 18. The apparatus of claim 17 further including means for heating washing liquid.
 19. The apparatus of claim 17 in which each roller contains grooves therein to define the said traversal path guiding means.
 20. The apparatus of claim 17 in which each roller is smooth surfaced and each pair of rollers is skewed.
 21. The apparatus of claim 20 further including power means to drive each roller in each said pair of rollers at the same rotational velocity.
 22. The apparatus of claim 16 wherein said washing tank includes a dividing means to separate the said tank into two washing areas connected by an opening, each washing area containing a pair of spaced, skewed, smooth-surfaced rollers, said washing tank further including means for introducing the said material from the second end of the first pair of rollers onto the first end of the second pair of rollers. 